I have long questioned whether copyright can be clearly enough defined to
be generally enforceable.

The same can be said about anything from murder to jaywalking.
This is why we have judges who generate case law.

IANAL but I see two qualitative differences: first, copyright involves
expressive rights, which in the US requires the courts to apply "strict
scrutiny" in some instances. If it applies, then strict scrutiny requires the
government to prove that the law meets stringent tests that don't apply to other
laws. If the law involves prior restraint, then it requires "super strict
scrutiny." (Source: wikipedia) I think the legal issues faced by the
government in the PGP case illustrate this.

Secondly, while their are clear definitions of murder and jaywalking, their may
be no clear definition of a copyrighted digital "copy." Once again, I would use
the broadcast flag is a good example of this.